The present invention relates to hybrid propulsion systems and more particularly to the management of a heat engine in a vehicle equipped with an electric infinitely variable transmission.
Hybrid propulsion systems are notably either of series type or of parallel type. In series-type systems, the heat engine is directly coupled with the electric engines, the assembly being connected to a common transmission shaft coupled with the driving wheels. In parallel-type systems, the heat engine drives some of the driving wheels whereas the electric engines drive the other driving wheels. For example, in the case of a vehicle with front-wheel drive, the heat engine usually drives the front axle system and the electric engines drive the rear axle system.
The category of series-type systems includes the particular case of systems that do not include any decoupling system for the heat engine with the electric engines and the wheels. A particular management of the different engine members is required to avoid jerky and uncomfortable driving conditions.
The patent applications FR2847015, FR2847014 and FR2847321 describe infinitely variable transmission systems with power bypass with electric speed regulator that can comprise one or two compound axle systems. The transmission systems described comprise two power channels over which the elements are distributed. One of the two channels comprises a reduction stage and control means making it possible to regulate the distribution of the power between the two channels. These three patent applications describe transmission systems comprising at least one compound axle system making it possible to immobilize at least one of the inputs of the transmission system. Neither of these two applications proposes any system making it possible to start the heat engine when the vehicle is rolling and without the use of a starter.
The patent application JP2000-238555 describes a hybrid system comprising a heat engine and two electric engines. One of the two electric engines is permanently assigned to the propulsion of the vehicle whereas the second engine is used mainly to start the heat engine. This patent application also describes a system for controlling the state of operation of a heat engine based on the detection of the temperature of the engine, its fuel consumption, vibrations and emitted polluting emissions. This device for determining the state of operation of the heat engine is limited by the influence of the environmental conditions on the various parameters analyzed and by the associated computation times and costs. The hybrid operating mode uses a drive train based on a decoupling between the heat engine and the wheel. The effectiveness of such a system is potentially limited.
Reciprocating propulsion systems are recognized as being particularly effective when the aim is to reduce the emissions of greenhouse gases and pollutants. However, even when they are used in a mostly electric operating mode, the reciprocating propulsion systems, for example hybrid power units, keep the internal combustion engine operating at low rotation speed. To achieve an objective of zero polluting emissions, notably in urban operation, it is advantageous to have a hybrid power unit that can operate in purely electric mode, but that remains capable of reactivating said heat engine in a manner that is imperceptible to the driver. While implementing such an operating mode is easier in the case of a parallel-type hybrid propulsion, the situation is quite different in the case of a series-type hybrid propulsion.
In practice, the absence of decoupling of the heat engine from the transmission in a system equipped with an infinitely variable transmission prohibits the stopping of the heat engine. In practice, stopping would involve immobilizing the transmission and eliminating the torque transmitted to the wheels. A system that makes it possible to circumvent this limitation is necessary, together with a means of bringing the heat engine to a rotation speed that is sufficient to take over from the electric engines in the propulsion of the vehicle, in an independent manner.